1. Technical field
The disclosure relates to an audio mixing device and method, and more particularly to a mixing device and method applied to an audio codec.
2. Background Art
An audio encoder/decoder (codec) can convert an analog audio signal (such as human voice and/or music sound), into a digital audio signal through an analog to digital converter (ADC), so as to transmit it to a subsequent stage device (such as a personal computer), for further audio processing.
In addition, the digital microphone is a device which has been used frequently in the field of audio processing in recent years. An ADC is built in the digital microphone, the digital microphone receives an analog audio signal, and the analog audio signal can be converted into a digital audio signal by the built-in ADC. This integration of elements saves space which can then be used to accommodate an external ADC, reducing the volume of related electronic elements and improving the capacity of the device to resist noise interference.
However, in order to improve the sound quality of a digital audio signal captured by a conventional external ADC or digital microphone, an over-sampling technology is usually used to capture the audio signal. The digital audio signal is then processed by a down sample filter to generate the output audio signal, so as to provide subsequent relevant applications. In this case, if the audio codec can receive the analog audio signal and the digital audio signal provided by the digital microphone, two down sample filters are needed to process audio signals from two different sources respectively. This increases the cost of the down sample filters.
U.S. Pat. No. 7,230,557B1 provides a solution to the problems described above. FIG. 1 is a schematic view of a conventional audio codec. The audio codec A1 includes: an ADC A10, a selecting module A30, and a down sample filter A40.
As shown in FIG. 1, the prior art uses the selecting module A30 to receive the digital audio signal transmitted by the ADC A10 and the digital audio signal transmitted by a digital microphone A20. A select signal is then used to select the output of the ADC A10 or the output of the digital microphone A20, and the selected output is transmitted to the down sample filter A40. Thus the audio codec Al can receive the digital audio signal transmitted by the digital microphone A20 at the same time as it receives the analog audio signal. The selecting module A30 selects the source to be transmitted to the down sample filter A40 as desired, so the additional down sample filter A40 is not needed, thereby reducing the cost of the circuit.
However, in actual application the user may need to mix the analog audio signal with the signal received and processed by the digital microphone in order to generate a mixed output signal. For example, in a live concert the background music is an analog audio signal, and a singer generates a digital audio signal through the digital microphone. In such cases, the analog background music and the digital audio signal of the singer must be combined and then output. In this case, since the above US patent can select and transmit only one output to the down sample filter for processing at a time because the selecting module is used, it is not capable of mixing the analog audio signal and the digital audio signal.
This is a problem that needs to be solved urgently in order to mix the analog audio signal and the digital audio signal.